Awake Spinal Fusion Is Associated with Reduced Length of Stay, Opioid Use, and Time to Ambulation Compared to General Anesthesia: A Matched Cohort Study

Abstract

Objective:

There is increasing interest in awake spinal fusion under spinal anesthesia (SA). Evidence supporting SA has been positive, albeit limited. The authors set out to investigate the effects of SA vs general anesthesia (GA) for spinal fusion procedures on length of stay (LOS), opioid use, time to ambulation (TTA), and procedure duration.

Methods:

The authors performed a retrospective review of a single surgeon’s patients who underwent lumbar fusions under SA vs GA. SA patients were compared to demographically matched GA counterparts undergoing comparable procedures. Analyzed outcomes include operative time, opioid usage in morphine milligram equivalents (MME), TTA, and LOS.

Results:

10 SA patients were matched to 10 GA counterparts. The cohort had a mean age of 66.77, a mean body mass index of 27.73 kg/m², and a median American Society of Anesthesiologists Physical Status Score of 3.00. LOS was lower in SA vs GA patients (12.87 vs 50.79 hours, p=0.001). Opioid utilization was reduced in SA vs GA patients (10.76 vs 31.43 MME, p=0.006). TTA was reduced in SA vs GA patients (7.22 vs 29.87 hours, p=0.022). Procedure duration was not significantly reduced in SA patients compared to GA patients (139.3 vs 188.2 minutes, p=0.089).

Conclusion:

These preliminary retrospective results suggest the use of SA rather than GA for lumbar fusions is associated with reduced hospital LOS, reduced opioid utilization, and reduced TTA. Future randomized prospective studies are warranted to determine if SA usage truly leads to these beneficial outcomes.

INTRODUCTION

There has been a marked rise in the volume of lumbar spine surgery for the treatment of lumbar degenerative disease, with incidence rising from 60.4 per 100,000 to 79.8 per 100,000 between 2004 and 2015 alone.^1–5 As the incidence of lumbar spine surgery has increased, so too has the sophistication of surgical techniques, as many surgeons now consider more minimally invasive approaches due to improved patient outcomes.^6–10 Surgical technique, though, is not the only domain in which spine surgery has seen evolution.

In recent years, there has been increasing, albeit limited, evidence to suggest that spine surgery under awake spinal anesthesia (SA), rather than general anesthesia (GA), may improve outcomes for patients undergoing lumbar spine surgery for degenerative disease.^11,12 Settings in which SA’s use in spine surgery has been studied include but are not limited to decompressive laminectomy and discectomy as well as spinal fusion.^13–16 Meta-analysis reveals that the majority of prior studies investigating the efficacy of SA have involved patients receiving decompressions, leaving a relative dearth of information on the use of SA for spinal fusions.¹

While there have been studies investigating the relative efficacies of SA and GA, these trials have yielded mixed results and frequently suffered from bias due to deviation from intended intervention as well as incomplete outcome data.¹⁷ Furthermore, many of these studies compared the anesthetic modalities with respect to operative metrics such as intraoperative hemodynamics or estimated blood loss, rather than patient outcomes such as opioid utilization or time to ambulation.¹⁸

Despite SA’s promise, and perhaps due to the sparsity of data surrounding it’s use, most clinicians consider GA the standard of care for the surgical management of lumbar degenerative disease. To better understand the relative advantages and disadvantages of SA in comparison to GA, we present a single-surgeon, retrospective, matched cohort study of patients receiving spinal and general anesthesia for comparable spinal fusion procedures to compare outcomes. The primary studied outcome is hospital length of stay (LOS), while secondary outcomes include opioid utilization, time to ambulation, and procedure duration.

METHODS

All patients were seen by the anesthesia preoperative team prior to surgery, and informed consent was obtained before every procedure. Institutional Review Board (IRB) approval was submitted to our ethics review committee and approved. Patient permission to publish deidentified data was not necessary, as this matched cohort study fell under the university’s IRB’s guide- lines for “exempt” patient research. Individual patient identifiers were removed from case examples and associated imaging.

Cohort Creation

The authors performed a single-center, single-surgeon, retrospective review of a prospectively collected database of patients undergoing lumbar spinal fusion for degenerative spinal disease under awake SA at a major academic research institution. Patients who received surgery between June of 2020 and June of 2022 were considered for inclusion. For each of these patients, a comparable patient that had received surgery under GA was sought out. A comparable patient was defined as having a similar age, similar body mass index (BMI), and receiving the same procedure at an identical or adjacent spinal level, using the same technique such as percutaneous vs minimally invasive fusion. While there were no hard cutoffs for differences in age between matched patients, the average discrepancy was 4.9 years. Similarly, there were no hard cutoffs for BMI difference in matched patients; the average discrepancy was 2.75 kg/m². Fusion techniques included percutaneous lumbar interbody fusion (percLIF) as well as minimally invasive transforaminal lumbar interbody fusion (MIS TLIF). Patients were matched in terms of which operative technique was used. There was no difference in admission and discharge pathways between the SA and GA cohorts. Patients all received identical truncal blocks, as described below, and all patients received local lidocaine prior to incision. The same expandable cage was used in all patients, and all patients received the same extent of facetectomy. All patients received appropriate preoperative counseling on the relative risks associated with surgery and respective anesthesia modality.

Baseline demographic information was collected. This included information such as age, sex, BMI, and medical comorbidities as well as American Society of Anesthesiologists Physical Status (ASA-PS). Perioperative, intraoperative, and postoperative data were collected. This included operative time, time to ambulation, opioid utilization, and length of stay (LOS). Operative time was determined on the basis of incision and closure and did not include factors such as induction of anesthesia. Time to ambulation was defined as the time between the patient’s arrival in the post anesthesia care unit (PACU) to their earliest recorded ambulation. Length of stay was defined as the time between the patient’s arrival in PACU to their time of discharge. This was done to control for variability in time between admission and procedure start. Opioid utilization was determined by consulting the medication administration records for 6 hours following arrival in the PACU. 6 hours was chosen over 12 or 24 hours because many patients receiving SA were discharged in under 12 hours, while only one patient was discharged in under 6 hours. Opioid usage was standardized into morphine milligram equivalents. Patients all received multimodal pain management

Erector Spinae Plane Block Technique

Erector spinae plane (ESP) block was performed preoperatively in the sitting position at the L4 spinal level. A curvilinear transducer was placed in a sagittal orientation over the spinous process and translated laterally until the transverse process was visible. A 21g Stimuplex (B-Braun, Bethlehem, PA) or SonoPlex II Facet (Pajunk, Alpharetta, GA) needle was then introduced in-plane from a cranial to caudal direction until the needle tip contacts the target transverse process at either its cranial or caudal border. Hydro-dissection and separation using normal saline was performed to confirm the proper injection plane below erector spinae and above the transverse process. Once the correct plane was identified, 10mL of liposomal bupivacaine (Exparel, Pacira Biosciences, Tampa, FL) admixed with 20mL 0.25% bupivacaine HCl (for a total of 30mL) was injected in the ipsilateral erector spinae plane. The needle was then removed, and the same process repeated on the contralateral side. Every included patient received bilateral ESP blocks.

Spinal Anesthesia Technique

Spinal anesthesia was performed in the sitting position with the patient’s spine flexed and legs hanging from the side of the bed. Next, the correct spinal level (generally L3-L4 bilaterally) and access site were identified via palpation. The patient was appropriately draped and the space between the spinal levels was cleaned with ChloraPrep. For the midline approach used in these cases, the approach to the intrathecal space was midline with a straight-line single shot. After infiltration, the spinal needle (Quincke 25-gauge 90 mm) was introduced into the skin angled cephalically. The needle passed through the superficial skin and subcutaneous fat. Once passed through the supraspinous, interspinous ligaments, and ligamentum flavum, the needle entered the epidural space. Usually, a “pop” is felt upon passing through the ligamentum flavum. For spinal anesthesia, the needle continued deeper until penetration of the dura-subarachnoid membranes. Once free-flowing CSF was seen, 10–15 mg 0.5% of isobaric bupivacaine was injected to achieve the anesthesia.

Outcome Measurements and Statistical Analysis

Patient demographics, age, BMI, and ASA-PS were treated as continuous variables. As not all demographic variables were found to be normally distributed per the Shapiro-Wilk test, demographics were compared with the non-parametric Wilcoxon rank-sum test. Cohort gender composition was analyzed by Fischer’s exact test. For measured outcomes, operative time, TTA, opioid utilization, and LOS were treated as continuous variables. Not all outcome variables were found to be normally distrusted per the Shapiro-Wilk test; outcomes were therefore analyzed by the non-parametric Wilcoxon rank-sum test. LOS was also analyzed via contingency testing for discharge occurring in greater than or less than 24 hours. In select circumstances, statistical outliers were removed. Criteria for outlier status was defined as being greater than two standard deviations above the group mean. 1 GA and 1 SA patient were removed from LOS calculations for their uncharacteristically high LOS. 1 GA patient was removed from TTA and opioid use calculations for uncharacteristically high TTA and opioid use. It is worth noting that all statistically significant findings would still retain statistical significance with inclusion of these outliers.

RESULTS

Cohort Matching and Demographics

The single surgeon performed 46 elective lateral approach lumbar fusions for degenerative spine disease (DSD) in the study period. 13 (17%) of these patients received their surgeries under SA. Of the 13 patients receiving awake spinal fusion, 3 patients could not be matched to a GA counterpart due to extreme demographic features, such as morbid obesity or octogenarian status, or medical comorbidities that were relative contraindications to GA such as severe cardiopulmonary disease. The remaining 10 patients that underwent lumbar spinal fusion for DSD under SA were successfully matched to GA patients receiving a comparable procedure at an adjacent or identical level. Cohort construction is summarized in Figure 1. The cohort had a mean age of 66.77 years, a mean BMI of 27.73 kg/m², and a median ASA-PS of 3.00; the groups had no statistically significant differences in demographic features. Cohort characteristics are summarized in Table 1. Standardized mean difference (d) and p values are shown.

Fig 1.

Patient selection resulting 10 total matched pairs

Table 1.

GA and SA Cohort Descriptive Statistics

Metric	GA Mean (95% CI)	SA Mean (95% CI)	p value	d value
Sex (% Female)	40%	50%	>0.999	-
Age (Years)	67.53 (62.16,72.91)	66.01 (61.36,70.65)	0.633	0.217
BMI (kg/m2)	28.54 (24.96,32.11)	26.91 (23.89,29.93)	0.443	0.352
Physical Status (ASA-PS)	2.80 (2.50,3.10)	* 3.00 (2.25, 3.00)	0.628	0.221
% Percutaneous	90%	90%	-	-
Number of Levels Treated	1.1 (0.87,1.33)	1.2 (0.90,1.50)	0.557	0.268

^*Median (IQR)

Case Presentation: Spinal Fusion Under General Anesthesia

A 68-year-old woman with a BMI of 21.62 kg/m² and a past medical history of intermittent asthma and depression (ASA-PS=3) presented with chief complaints of lower back pain and bilateral radiculopathy refractory to conservative management. Imaging revealed spondylolisthesis at the level of L4-L5 with severe spinal stenosis (Fig 2). The patient elected to undergo L4-L5 minimally invasive lumbar interbody fusion under GA.

Fig 2.

GA Patient Preoperative Imaging (A. Flexion X-Ray, B. Extension X-Ray, C. T2 Weighted Sagittal MRI, D. T2 Weighted Axial MRI)

The patient was brought into the operating theater. General endotracheal anesthesia was obtained. An ultra-minimally invasive, percutaneous lumbar interbody fusion was performed, and good correction of spondylolisthesis was observed. There were no intraoperative complications.

The patient utilized 19 MME for pain control in the operative and postoperative days. The patient was able to ambulate 5.07 hours after arrival in the post-anesthesia care unit (PACU); she was discharged 53.23 hours after arrival in the PACU for a total hospital LOS of 59.61 hours. Postoperative changes are shown (Fig 3).

Fig 3.

GA Patient Whole Spine X-Rays with Spinopelvic Parameters (A. Preoperative, B. Postoperative). Preoperative: PI=60, PT=23, SS=37, LL=47, SVA=+43. Postoperative: PI=61, PT=21, SS=40, LL=49, SVA=+67.2

Case Presentation: Spinal Fusion Under Spinal Anesthesia

A 67-year-old woman with a BMI of 23.58 kg/m² and past medical history of osteoporosis and renal cell carcinoma (ASA-PS=3) presented with chief complaints of lower back pain and bilateral radiculopathy refractory to conservative management. Imaging revealed spondylolisthesis at the level of L4-L5 with instability with extension (Fig 4). The patient elected to undergo L4-L5 minimally invasive lumbar interbody fusion under SA.

Fig 4.

SA Patient Preoperative Imaging (A. Flexion X-Ray, B. Extension X-Ray, C. T2 Weighted Sagittal MRI, D. T2 Weighted Axial MRI)

The patient was brought into the operating theater. General endotracheal anesthesia was not obtained, as the patient remained conscious with spontaneous respiration throughout the operation. Spinal anesthesia was obtained with 0.5% isobaric bupivacaine. An ultra-minimally invasive, percutaneous lumbar interbody fusion was performed, and good correction of spondylolisthesis was observed. There were no intraoperative complications.

The patient utilized 10.7 MME for pain control in the operative and postoperative days. The patient was able to ambulate 4.37 hours after arrival in the PACU; she was discharged 8.68 hours after arrival in the PACU for a total hospital LOS of 14.25 hours. Postoperative changes are shown (Fig 5).

Fig 5.

SA Patient Whole Spine X-Rays with Spinopelvic Parameters (A. Preoperative, B. Postoperative). Preoperative: PI=54, PT=15, SS=37, LL=60, SVA=−7.12. Postoperative: PI=54, PT=16, SS=38, LL=56, SVA=+5.65

Patient Outcomes

When compared to their GA counterparts, SA patients had a reduced hospital length of stay (12.87 vs 50.79 hours, p=0.001). SA patients also required fewer opioids than their GA counterparts (10.76 vs 31.43 MME, p=0.006). TTA was reduced in SA patients compared to GA patients (7.22 vs 29.87 hours, p=0.022). Procedure duration was not statistically significantly reduced in SA patients compared to GA patients (139.3 vs 188.2 minutes, p=0.089). No patients in the SA cohort had any 90-day readmissions. One patient in the GA cohort had multiple readmission due to bradycardia and syncope in the 90-day postoperative period. Results are summarized in Table 2 and Figure 6.

Table 2.

GA and SA Patient Outcomes

Metric	GA Mean (95% CI)	SA Mean (95% CI)	p value
Hospital Length of Stay (Hours)	50.79 (33.86,78.73)	12.87 (2.16,23.58)	0.001
Postoperative Opioid Use (MME)	31.43 (19.03,43.84)	10.76 (4.51, 17.01)	0.006
Time to Ambulation (Hours)	29.87 (7.047,52.69)	7.22 (1.93,12.51)	0.022
Procedure Duration (Minutes)	188.2 (136.1,240.3)	139.3 (118.1,161.7)	0.089

Fig 6.

Summary of Patient Outcomes (A. Length of Stay, B. 24 Hour Discharge, C. Opioid Use, D. Time to Ambulation, E. Procedure Duration). Length of stay was statistically significantly reduced in SA patients (50.79 vs 12.87 hours, p=0.010). SA patients are statistically significantly more likely to be discharged within 24 hours of PACU arrival (p=0.050). Postoperative opioid utilization is statistically significantly reduced in SA patients (31.42 vs 10.76 MME, p=0.003). Time to ambulation is statistically significantly reduced in SA patients (29.87 vs 7.22 hours, p=0.032). Procedure duration is non-statistically significantly reduced in SA patients (188.2 vs 139.9 minutes, p=0.069).

DISCUSSION

Advances in the Field of Awake Spine Surgery

There has been significant increase in the occurrence of awake spinal surgery over the past years¹. Many factors have led to this increase, yet it is largely due to changes in route of administration of anesthesia as well as advances in surgical technique. Despite these advancements, GA is still the most prevalent anesthetic technique, with up to 98% of cases occurring under GA.¹⁹ GA is not without drawbacks, however. GA, while generally safe, is associated with a significant increase in postoperative nausea and vomiting (at least when performed with inhaled anesthetics) and may be associated with other, more serious, complications as well.²⁰ To decrease complication rates, protocols utilizing regional anesthetic techniques, such as the erector spinae plane (ESP) block and thoracolumbar interfascial plane (TLIP) blocks, have been implemented.^14–16 Surgeries performed under spinal anesthesia have been found, by meta-analysis, to be associated with reduced incidence of postoperative nausea and vomiting, shorter length of stay, and lower intraoperative blood loss.^12,21 While SA is what ultimately allows patients to receive surgery while awake, the development of minimally invasive spine surgery has also been a critical component in enabling the development of awake spine surgery. Minimally invasive spine surgery not only facilitates awake spine surgery through reducing the psychological burden on the patient, but also is associated with reduced blood loss, reduced length of stay, less postoperative disability, and fewer complications such as dural injury or wound infection.^12,21–23 It is worth noting, however, that these benefits are, at times, at the expense of increased fluoroscopy times.⁶

Awake spine surgery has been used for a wide variety of spinal procedures, and commonly performed awake spinal surgeries include, but are not limited to laminectomy, discectomy, anterior cervical discectomy and fusion, lumbar fusion, and dorsal column stimulator placement.²⁴

Preliminary work on the use of SA for surgical management of DSD has been tentatively promising; previous studies have shown that with SA, there is improved postoperative analgesia, decreased intraoperative complications, reduced economic costs, and improved perioperative outcomes.^{11,19,24–34} Although there is growing evidence favoring the use of SA over GA, the relative strengths of each have not yet been consistently identified. Thus, the authors set out to perform a retrospective matched cohort study to help determine the relative strengths and weaknesses of SA and GA. The cohorts were constructed of SA patients who had well controlled GA counterparts. Although 10 patients from each cohort were analyzed, it is worth noting that more than 10 patients underwent SA during the study period. It was impossible, however, to match three of these patients from the larger SA group to a comparable GA patient. This is because the SA patients disproportionately carried medical comorbidities that put them at increased risk for GA’s potential cardiopulmonary or cognitive complications, thereby making SA the safest choice for this population.^20,21,35,36 Examples of such patients include octogenarians as well as patients with severe cardiovascular disease and BMIs greater than 40 kg/m². Within the matchable cohort, however, SA appears to demonstrate the capacity to improve some patient outcomes.

Study Results

Some of the most noteworthy findings of this study surround our primary objective, SA’s impact on hospital LOS when compared to GA. Our study demonstrated that SA may reduce hospital length of stay and may increase the likelihood of being discharged within 24 hours of arrival in the PACU. This is particularly meaningful in the context of the current healthcare landscape in the wake of COVID-19, where healthcare worker shortages make it challenging to maintain prior operative volume.^37,38 In this sense, SA’s capacity to increase same-day discharges make it a powerful tool in a congested healthcare system. Our study additionally suggested that SA is associated with decreased TTA, which likely helps contribute to this decreased discharge time. This finding is consistent with prior literature.^39,40

Another significant finding of our study was SA patient’s reduced opioid utilization. It is perhaps worth noting, that neither the SA nor the GA cohorts used a tremendous quantity of opioids compared to what is often seen following lumbar fusion.⁴¹ One factor that likely led to minimal opioid utilization in both the SA and GA cohorts is the fact that all patients studied received an ESP block and 9 out of 10 matched pairs underwent a newer ultra-minimally invasive technique called the percutaneous lumbar interbody fusion (percLIF). Previous studies have illustrated the ESP’s ability to reduce opioid utilization, with one notable study of nearly 700 patients which revealed a significant decrease in morphine utilization in patients who underwent ESP in the first 24 hours following surgery compared to a control group.⁴² Our findings show, however, that even in the presence of an ESP block, surgery under SA is associated with reduced postoperative opioid utilization. Other findings of this study include SA’s capacity to reduce hospital length of stay, which is supported by current literature.¹¹

Other findings of SA patients reduced procedure duration did not meet criteria for statistical significance. Nevertheless, it is the author’s belief that these findings warrant further study. For example, while not previously shown through a matched cohort construct, SA’s capacity to reduce operative time has been demonstrated by meta-analysis.^11,31 It is possible that reduced operative time is a result of increased surgeon focus in the setting of an awake patient. There are several other, well documented phenomena that may also contribute to this finding, and they are described well in meta-analysis by Urick et. al.¹¹

Our study additionally adds to the sparse body of evidence supporting the use of SA for spinal fusions, as the majority of literature surrounding SA investigates is utility in decompressions.¹¹

Limitations

The most significant limitation of this study was the small size of the cohort, featuring only 10 matched pairs for a total of 20 studied patients. Despite this, SA did demonstrate statistically significant effects in reducing length of stay, opioid utilization, and time to ambulation.

Another important limitation is the possible selection bias inherent to a retrospective study. To reduce this bias as much as possible, a matched-cohort design was chosen in order to best control for demographic factors, such as age, BMI, and ASA-PS, as well as surgical factors such as surgical technique and level of fusion. Despite careful efforts to control for these variables, a prospective randomized control trial is necessary to achieve truly blinded control. Additionally, opioid utilization was only studied in the immediate, six-hour postoperative setting due to the brief hospital stays of many patients. Future work must seek to investigate at home opioid utilization following discharge. Long term clinical status was not investigated due to the recency of surgery in many of the included patients.

Lastly, this retrospective non-randomized study may suffer from indication bias. That is, the patients selected to receive SA were consciously chosen, therefore they possess meaningful differences from GA patients. This concern is supported by the fact that 3 of the 13 identified awake fusion patients were unable to be matched to a GA counterpart. Reassuringly, however, we would not expect a disproportionately comorbid patient group to display superior outcomes if it were not for differences in the experimental variable of anesthesia type; we therefore still conclude that SA demonstrates great promise. Only a prospective, randomized control trial will truly eliminate the potential for confounding-by-indication.

CONCLUSION

Although the study was performed retrospectively in a small cohort, we demonstrate that SA is a safe, effective anesthetic technique for lumbar spinal fusion. Furthermore, these preliminary retrospective results suggest the use of SA rather than GA for lumbar fusions is associated with shorter hospital length of stay, reduced opioid utilization, and reduced time to ambulation compared to a matched cohort. Future randomized prospective studies are warranted to determine if SA usage truly leads to these beneficial patient outcomes.